Growth and photosynthetic activities of wild-type and antenna-deficient mutant strains of Rhodobacter capsulatus

Cells of Rhodobacter capsulatus wild-type strains (37b4, B 10) and mutant strains, lacking lightharvesting (LH) complex II (B800–850) and defective in formation of LH I (B870) complex U 43 (pTXB 87), U43 (pTXA6-10)] were grown photosynthetically at high and low light intensities in a turbidostate. The mutant strain U43 (pTXA6-10), lacking any LH system, was able to grow at high and low light intensities with doubling times of 4.6 and 9.8 h, respectively. In this mutant the concentration of photochemical reaction centers (RC) per cell and per membrane protein was several times higher than in wild type cells, but the bacteriochlorophyll content, the size of the photosynthetic unit and the rate of photophosphorylation were lower than in wild type cells. Reversible bleaching of reaction center and photophosphorylation were measured under different excitation light intensities. The charge recombination in the RC between the primary donor and Q_B was very slow in the mutant strains. Two membrane fractions differing in absorption spectra and light saturation behaviour of reversible bleaching and photophosphorylation were isolated from the mutant strains. The experimental data indicate that photosynthetic units of different composition and/or organization are present in the mutant cells.Abbreviations DSM Deutsche Sammlung von Mikroorganismen, Braunschweig